Several Iranian boats approached and attempted to impede a British commercial vessel sailing through the Strait of Hormuz, but the Iranian vessels were driven away by a British military ship, a senior U.S. defense official and a British government spokesperson said.
Iran's Islamic Revolutionary Guard Corps denied any encounters with foreign vessels within the last 24 hours.
According to the U.K. and U.S. officials, no shots were fired in the incident, which came amid escalating tensions in the region.
"Contrary to international law, three Iranian vessels attempted to impede the passage of a commercial vessel, British Heritage, through the Strait of Hormuz," according to a statement from a U.K. government spokesperson distributed through that country’s Ministry of Defense press office.
The statement said that the HMS Montrose warship "was forced to position herself between the Iranian vessels and British Heritage and issue verbal warnings to the Iranian vessels, which then turned away."
"We are concerned by this action and continue to urge the Iranian authorities to de-escalate the situation in the region," the U.K. government spokesperson said.
The senior U.S. defense official said armed Iranian boats approached the British tanker and were attempting to drive it into territorial waters but were pushed away by the HMS Montrose, which was around 4 miles behind the tanker.
Capt. Bill Urban, a spokesman for the U.S. Central Command, said in a statement that the U.S. military was "aware of the reports of Islamic Revolutionary Guard Corp Navy's FAC/FIAC harassment and attempts to interfere with the passage of the U.K.-flagged merchant vessel British Heritage today near the Strait of Hormuz."
The Islamic Revolutionary Guard Corps — a powerful military unit with deep economic resources that answers only to the country's supreme leader — denied the U.S. and U.K. version of the events.
"During the last 24 hours there have not been any encounters with foreign vessels, including English boats," the IRGC said in a statement.
In the event a command was issued to seize any foreign vessel, it "is able to act promptly" and "decisively," the statement added.
Iranian Foreign Minister Mohammad Javad Zarif told local media that "the claims that are being made is just to create tension and these claims are worthless," and that the claims of interference were rejected by the Revolutionary Guard.
The incident is the latest to be reported near the Strait of Hormuz, a strategic waterway off Iran's coast which separates the Persian Gulf and the Gulf of Oman. A third of the world's seaborne oil shipments, and 20 percent of oil traded worldwide, pass out of the Persian Gulf through the Strait.
Pressure in the region has been building since President Donald Trump took office, and the administration withdrew from the 2015 nuclear agreement and imposed punishing sanctions on the country. The administration has also designated the IRGC as a foreign terrorist organization. Last month, Trump signed an executive order putting in place new sanctions.
The IRGC said it shot down a U.S. surveillance drone last month. Iranian officials claimed they shot down the unmanned aircraft after it entered Iranian airspace, but the United States has disputed that and said it was in international airspace above the Strait of Hormuz.
"Threats to international freedom of navigation require an international solution. The world economy depends on the free flow of commerce, and it is incumbent on all nations to protect and preserve this linchpin of global prosperity," Urban said in the statement.
There were no deaths reported in that incident, which involved a Japanese and a Norwegian vessel. One person aboard the Japanese tanker, the Kokuka Courageous, suffered minor injuries, the vessel’s management firm has said.
U.S. officials have alleged hostile behavior by Iranian forces and proxy groups. The U.S. has also accused Iran of moving missiles and missile components through the region's waterways for years, shipping missiles to the Houthis in Yemen and others.
After the U.S. drone was shot down, Trump tweeted that the U.S. was "cocked & loaded" to retaliate with military strikes on Iranian targets, but he said he called off the action after being told 150 people could die.
Iran said Sunday it would roll back its commitments made in the nuclear deal it signed with the U.S. and other powers, vowing to enrich uranium beyond the cap set by the 2015 agreement.
Brian Hook, the U.S. special representative for Iran, told Al-Jazeera that the U.S. is seeking a Senate-approved agreement to replace the nuclear deal.
On Tuesday, U.S. Marine Gen. Joseph Dunford, the chairman of the Joint Chiefs of Staff, said the U.S. wants to build a maritime coalition to stop attacks on tankers in the waters off Iran.
CORRECTION (July 11, 1:20 a.m.): A previous version of this article misspelled the first name of a U.S. Central Command spokesman. He is Capt. Bill Urban, not Bull.